Plugging and sealing subterranean formations

ABSTRACT

A subterranean formation sealant includes a mixture of an aqueous colloidal dispersion including silica nanoparticles and a C6-C12 fatty acid. Heating the sealant above 70° C. initiates gelation of the sealant. Sealing an opening in a water or gas producing zone in a subterranean formation includes providing a sealant including a mixture of a colloidal dispersion including silica nanoparticles and a C6-C12 fatty acid to the water or gas producing zone, initiating gelation of the sealant in situ, and solidifying the sealant in the water or gas producing zone to yield a set gel, thereby sealing the opening in the water or gas producing zone.

TECHNICAL FIELD

This document relates to methods and compositions for plugging andsealing unwanted water and gas producing zones in subterraneanformations.

BACKGROUND

Excessive water production greatly affects the economic life ofproducing wells.

High water cut largely affects the economic life of producing wells andmay be responsible for oil field related damage mechanisms, such asscale deposition, fines migration, asphaltene precipitation, corrosion,and the like, leading to increased operating costs for separating,treating, and disposing of the produced water according to environmentalregulations. Though a variety of chemicals are used by the industry tocontrol water production, many are not environmentally acceptable inregions with strict environmental regulations.

SUMMARY

In a first general aspect, a subterranean formation sealant includes amixture of an aqueous colloidal dispersion including silicananoparticles and a C6-C12 fatty acid. Heating the sealant above 70° C.initiates gelation of the sealant.

In a second general aspect, sealing an opening in a water or gasproducing zone in a subterranean formation includes providing a sealantincluding a mixture of a colloidal dispersion including silicananoparticles and a C6-C12 fatty acid to the water or gas producingzone, initiating gelation of the sealant in situ, and solidifying thesealant in the water or gas producing zone to yield a set gel, therebysealing the opening in the water or gas producing zone.

Implementations of the first and second general aspect may include oneor more of the following features.

A viscosity of the sealant at 20° C. is typically less than 5 cP. A pHof the sealant is in a range of 1 to 6.

The colloidal dispersion includes at least one of a salt and awater-miscible organic solvent. A size of the silica nanoparticles is ina range of 1 nm to 500 nm. A concentration of the silica nanoparticlesin the colloidal dispersion is in a range of 10 wt % to 50 wt %. A pH ofthe aqueous colloidal dispersion is in a range of 8 to 11.

A ratio of the C6-C12 fatty acid to the colloidal dispersion istypically in a range of 0.25 vol % to 5 vol %. The C6-C12 fatty acidincludes, consists essentially of, or consists of C6-C8 fatty acid. TheC6-C8 fatty acid typically includes one or more of hexanoic acid,heptanoic acid, and octanoic acid.

Implementations of the second general aspect may include one or more ofthe following features.

Initiating gelation may include heating the sealant in situ. Heating thesealant in situ may include heating the sealant via conduction orconvection with heat contained in the subterranean formation.

The opening is a bottom water coning or cresting, a channel behind acasing, a channel from an injector, a cross flow, or a natural fracture.

In some implementations, the second general aspect includes decreasing apH of the sealant to accelerate the gelation of the sealant. In someimplementations, the second general aspect includes increasing atemperature of the sealant to accelerate the gelation of the sealant.Some implementations of the second general aspect include increasing aconcentration of the silica nanoparticles in the sealant or aconcentration of the C6-C12 fatty acid in the sealant to accelerate thegelation of the sealant.

The disclosed sealant is advantageously water-based and includesenvironmentally acceptable components. The silica nanoparticles areenvironmentally benign, and the C6-C12 fatty acid is biodegradable andenvironmentally acceptable. In addition, the gelation time of thedisclosed sealant can be advantageously controlled by, for example,adjusting the concentration of the C6-C12 fatty acid, allowing apredictable and controllable pumping time ranging from a few minutes toseveral hours at a given temperature. Thus, the sealant remains pumpablefor a sufficient length of time for placement and develops the networkstructure that leads to gelation over a predictable length of time. Theset gel, which appears as a crystalline solid, advantageously remainshomogeneous and remains in place under confined conditions, such asfractures and pore spaces.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts an exemplary system for delivering fluid to a borehole ina subterranean formation.

FIG. 2 is a flowchart showing operations in an exemplary process forsealing an opening in a water or gas producing zone in a subterraneanformation.

DETAILED DESCRIPTION

FIG. 1 depicts exemplary system 100 for delivering fluid to borehole 102in subterranean formation 104. In some embodiments, borehole 102 is awellbore. Fluid from source 106 is pumped via pump 108 through line 110and enters borehole 102 through pipe 112. The fluid may be a sealantprovided to subterranean formation 104 via pipe 112 to plug or sealwater or gas producing zone 114. The water or gas producing zone to besealed may be referred to as a “target zone.” The sealant may be placedas a single solution into the water bearing zones of subterraneanformation 104 around wellbore 102, and allowed to propagate through therock matrix. The sealant may be a low viscosity solution. In oneembodiment, a viscosity of the sealant is less than 5 cP at 20° C. Inone example, sealant provided to subterranean formation 104 via system100 effectively prevents water flow in sandstone and carbonateformations at temperatures in a range of 70° C. to 150° C. An initiallow viscosity of the sealant allows for low injection pressures.

The sealant includes a mixture of a colloidal dispersion comprisingmetal oxide nanoparticles and an activator. The metal oxidenanoparticles may be silica nanoparticles. The activator is a C6-C12fatty acid or a mixture thereof. In some embodiments, the fatty acidincludes, consists essentially or, or consists of at least one ofhexanoic acid, heptanoic acid, octanoic acid, nonanoic acid, decanoicacid, undecanoic acid, and dodecanoic acid. In certain embodiments, thefatty acid includes, consists essentially of, or consists of at leastone of hexanoic acid, heptanoic acid, and octanoic acid. Silicananoparticles are environmentally benign, and C6-C12 fatty acid isbiodegradable and environmentally acceptable.

The silica nanoparticles in the colloidal dispersion have a size in arange of 1 nm to 500 nm. A smaller particle size of the silicananoparticles typically promotes faster gelling of the sealant. Aconcentration of the silica nanoparticles in the colloidal dispersion isin a range of 10 wt % to 50 wt %. A higher concentration of the silicananoparticles typically promotes faster gelling of the sealant. In someembodiments, the colloidal dispersion includes a salt. Examples ofsuitable salts include sodium chloride, potassium chloride, calciumchloride, sodium bromide, calcium bromide, sodium formate, potassiumformate, cesium formate, and mixtures thereof. In some embodiments, thecolloidal dispersion includes a water-miscible organic solvent. Examplesof suitable water-miscible organic solvents include but not limited tomethanol, ethanol, propanol, butanol, ethyl acetate, dimethyl sulfoxide,dimethyl formamide, acetone, and mixtures thereof. The totalconcentration of silica in the colloidal dispersion is 10 wt % to 50 wt%. A pH of the colloidal dispersion is typically in a range of 8 to 11.

When the pH of the colloidal dispersion is at least 8, the colloidaldispersion typically remains in liquid form, with electrical repulsionbetween charged particles stabilizing the dispersion. Disturbing thecharge balance of the colloidal dispersion may cause the silicananoparticles to aggregate, resulting in the formation of a gel beforethe C6-C12 fatty acid is combined with the colloidal dispersion.Disturbing the charge balance may include at least one of: removingwater from the colloidal dispersion, changing the pH of the colloidaldispersion, adding a salt to the colloidal dispersion, and adding awater-miscible organic solvent to the dispersion. Examples of suitablesalts include sodium chloride, potassium chloride, calcium chloride,sodium bromide, calcium bromide, sodium formate, potassium formate,cesium formate, and mixtures thereof. Examples of suitablewater-miscible organic solvents include methanol, ethanol, propanol,butanol, ethyl acetate, dimethyl sulfoxide, dimethyl formamide, acetone,and mixtures thereof.

The C6-C12 fatty acid is a liquid at room temperature and includes atleast one of hexanoic acid, heptanoic acid, and octanoic acid. Thesefatty acids can lower the pH of the colloidal dispersion and hence causegelation. A ratio of the C6-C12 fatty acid to the colloidal dispersionis in a range of 0.25 vol % to 5 vol %. Increasing a concentration ofthe C6-C12 fatty acid in the sealant typically promotes faster gellingof the sealant.

The colloidal dispersion and the C6-C12 fatty acid are combined to yieldthe sealant. The sealant typically has a viscosity in a range of 1 cP to1000 cP or 1 cP to 5 cP at a temperature of 20° C. Concentration of thecolloidal dispersion, the C6-C12 fatty acid, or both may be varied asneeded for particular applications. In one example, increasing aviscosity of the sealant may facilitate placement of the sealant andcontrol of its location, as well as provide viscous diversion to coverlonger intervals.

Combining the colloidal dispersion and the C6-C12 fatty acid reduces thepH of the colloidal dispersion from at least 8 to below 8. In someembodiments, decreasing the pH of the colloidal dispersion from at least8 to below 8 initiates gelation of the sealant when the temperature ofthe sealant is in a range of 5° C. to 300° C. In some embodiments,gelation is initiated due at least in part to the formation temperature,and an increase in the temperature of the sealant that occurs in theformation due to the formation temperature. Thus, in situ gelationoccurs, via conduction or convection with heat contained in thesubterranean formation, thereby sealing an opening in a water or gasproducing zone in the subterranean formation.

Gelation is believed to occur at least in part as a result of collisionof the silica nanoparticles, which aggregate into long chain-likenetworks, forming a gel. Collision of the silica nanoparticles isincreased by reduction in pH of the colloidal dispersion, an increase intemperature of the sealant, or both. Not to be bound by theory, it isbelieved that collision of the silica nanoparticles results in theformation of siloxane bonds (Si—O—Si) between silica nanoparticles. Theformation of siloxane bonds may be catalyzed by the presence ofhydroxide ions. Gelation results in the formation of a set gel whenaggregate formation is complete, yielding uniform three-dimensionalnetworks of long, bead-like strings of silica nanoparticles.

Gelation may occur during static aging of the sealant. In someembodiments, gelation of the sealant is accelerated by decreasing the pHof the sealant. Typically, the more acidic the pH of the sealant, thefaster gelation occurs. In some embodiments, the gelation of the sealantis accelerated by increasing the temperature of the sealant. Thetemperature of the sealant during gelation may be in a range of 5° C. to300° C., 5° C. to 250° C., or 5° C. to 200° C. In some embodiments, thegelation of the sealant is accelerated by increasing the concentrationof C6-C12 fatty acid in the sealant. The sealant can be solidified in awellbore over a length of time as gelation progresses, advantageouslyallowing the sealant to remain pumpable for a sufficient and predictablelength of time ranging from about 30 minutes to about 48 hours at agiven temperature, while a network structure develops.

Gelation of the sealant yields a set gel in the form of a solid gel or asemi-solid gel. In some embodiments, the set gel is in the form of asolid crystalline material. The length of time between initiation ofgelation and formation of the set gel depends at least in part on the pHof the sealant, the temperature of the sealant, the concentration ofsilica nanoparticles in the colloidal dispersion, and the ratio ofC6-C12 fatty acid to the silica nanoparticles. A set gel may function asan efficient conformance product for plugging and sealing an openingsuch as a bottom water coning or cresting, a channel behind a casing, achannel from an injector, a cross flow, or a natural fracture. The setgel remains as a semi-solid gel or solid gel in the opening, therebyreducing production of unwanted water or gas. In some embodiments, theset gel effectively prevents water and gas flow in sandstone formationsat 70° C. to 150° C. In some embodiments, the set gel is stableindefinitely at a temperature in a range of 5° C. to 200° C. In certainembodiments, the set gel is stable essentially indefinitely at atemperature up to 260° C. No precipitation of the silica nanoparticlesis observed during gel formation or at elevated temperatures.

FIG. 2 is a flowchart showing operations in an exemplary process forsealing an opening in a water or gas producing zone in a subterraneanformation. The opening may be a bottom water coning or cresting, achannel behind a casing, a channel from an injector, a cross flow, or anatural fracture. In 202, a sealant including a mixture of a colloidaldispersion and C6-C12 fatty acid is provided to the water or gasproducing zone. The colloidal dispersion includes silica nanoparticles.In 204, gelation of the sealant is initiated in situ. In 206, thesealant is solidified in the water or gas producing zone to yield a setgel, thereby sealing the opening in the water or gas producing zone. Insome embodiments, an order of the operations in process 200 may bealtered. In some embodiments, operations in process 200 may be omittedor added.

In some embodiments of process 200, initiating gelation includes heatingthe sealant in situ. Heating the sealant in situ includes heating thesealant via conduction or convection with heat contained in thesubterranean formation. Gelation of the sealant may be accelerated bydecreasing a pH of the sealant, increasing a temperature of the sealant,increasing a concentration of the silica nanoparticles in the sealant,or increasing a concentration of the C6-C12 fatty acid in the sealant.The set gel may be in the form of a solid gel or a semi-solid gel. A setgel in the form of a solid gel may have the appearance of a crystallinesolid. The set gel may effectively prevent water and gas flow insandstone and carbonate formations at a temperature in a range of 70° C.to 150° C.

Example

2 mL of SABIC FATTY ACID C6-C8 (available from SABIC Chemicals) wascombined with 100 mL of an alkaline, aqueous colloidal dispersion ofsilica nanoparticles (IDISIL SI 4545, available from Evonik Industries),and the dispersion was mixed well with a stirrer. SABIC FATTY ACID C6-C8includes a mixture of 35-45% hexanoic acid and 55-65% octanoic fattyacid. Table 1 lists properties of IDISIL SI 4545.

TABLE 1 Properties of IDISIL SI 4545 Specific Particle size % pH gravityVisual Product titrated (nm) SiO₂ (25° C.) (g/mL) appearance IDISIL 4545 11 1.32 white/off-white SI 4545

Other suitable colloidal dispersions include CEMBINDER 17 and CEMBINDER50, available from AkzoNobel. Properties of CEMBINDER 17 and CEMBINDER50 are listed in Table 2.

TABLE 2 Properties of CEMBINDER 17 and CEMBINDER 50 SiO₂ Na₂O Vis-Density Average (wt (wt cosity (gm/ size Product %) %) pH (cP) cm³) (nm)CEMBINDER 50 15% 0.4% ~10 3.0 1.1 5 CEMBINDER 17 40% 0.3% ~9.4 6.0 1.117

The resulting sealant was then subjected to static aging at 120° C. for16 hours. Gelation resulted in a set gel after 16 hours of static aging.The set gel was a solid gel having the appearance of a crystallinesolid.

Definitions

In this document, the terms “a,” “an,” or “the” are used to include oneor more than one unless the context clearly dictates otherwise. The term“or” is used to refer to a nonexclusive “or” unless otherwise indicated.The statement “at least one of A and B” has the same meaning as “A, B,or A and B.” In addition, it is to be understood that the phraseology orterminology employed in this disclosure, and not otherwise defined, isfor the purpose of description only and not of limitation. Any use ofsection headings is intended to aid reading of the document and is notto be interpreted as limiting; information that is relevant to a sectionheading may occur within or outside of that particular section.

Values expressed in a range format should be interpreted in a flexiblemanner to include not only the numerical values explicitly recited asthe limits of the range, but also to include all the individualnumerical values or sub-ranges encompassed within that range as if eachnumerical value and sub-range is explicitly recited. For example, arange of “about 0.1% to about 5%” or “about 0.1% to 5%” should beinterpreted to include not just about 0.1% to about 5%, but also theindividual values (for example, 1%, 2%, 3%, and 4%) and the sub-ranges(for example, 0.1% to 0.5%, 1.1% to 2.2%, 3.3% to 4.4%) within theindicated range. The statement “about X to Y” has the same meaning as“about X to about Y,” unless indicated otherwise. Likewise, thestatement “about X, Y, or about Z” has the same meaning as “about X,about Y, or about Z,” unless indicated otherwise. The term “about” canallow for a degree of variability in a value or range, for example,within 10%, within 5%, or within 1% of a stated value or of a statedlimit of a range.

The term “fluid” refers to gases, liquids, gels, slurries with a highsolids content, and critical and supercritical materials.

The term “sealant” refers to a material provided to a wellbore orsubterranean formation that inhibits or prevents flow of a fluid betweentwo locations, such as between portions of a wellbore, between portionsof a subterranean formation, between a portion of a wellbore and aportion of a subterranean formation, or between a portion of a wellboreand a portion of a tubular string in the wellbore.

The term “subterranean formation” refers to any material under thesurface of the earth, including under the surface of the bottom of theocean. For example, a subterranean formation can be any section of awellbore and any section of a subterranean petroleum- or water-producingformation or region in fluid contact with the wellbore. In someexamples, a subterranean formation can be any below-ground region thatcan produce liquid or gaseous petroleum materials, water, or any sectionbelow-ground in fluid contact therewith. For example, a subterraneanformation can be at least one of an area desired to be fractured, afracture, or an area surrounding a fracture, and a flow pathway or anarea surrounding a flow pathway, where a fracture or a flow pathway canbe optionally fluidly connected to a subterranean petroleum- orwater-producing region, directly or through one or more fractures orflow pathways.

Other Embodiments

It is to be understood that while embodiments have been described inconjunction with the detailed description thereof, the foregoingdescription is intended to illustrate and not limit the scope of theinvention, which is defined by the scope of the appended claims. Otheraspects, advantages, and modifications are within the scope of thefollowing claims.

What is claimed is:
 1. A subterranean formation sealant comprising amixture of: an aqueous colloidal dispersion comprising silicananoparticles; and a C6-C12 fatty acid, wherein heating the sealantabove 70° C. initiates gelation of the sealant.
 2. The sealant of claim1, wherein a viscosity of the sealant at 20° C. is less than 5 cP. 3.The sealant of claim 1, wherein the colloidal dispersion comprises atleast one of a salt and a water-miscible organic solvent.
 4. The sealantof claim 1, wherein a size of the silica nanoparticles is in a range of1 nm to 500 nm.
 5. The sealant of claim 1, wherein a concentration ofthe silica nanoparticles in the colloidal dispersion is in a range of 10wt % to 50 wt %.
 6. The sealant of claim 1, wherein the C6-C12 fattyacid consists essentially of C6-C8 fatty acid.
 7. The sealant of claim1, wherein the C6-C8 fatty acid comprises one or more of hexanoic acid,heptanoic acid, and octanoic acid.
 8. The sealant of claim 1, wherein apH of the aqueous colloidal dispersion is in a range of 8 to
 11. 9. Thesealant of claim 1, wherein a ratio of the C6-C12 fatty acid to thecolloidal dispersion is in a range of 0.25 vol % to 5 vol %.
 10. Thesealant of claim 1, wherein a pH of the sealant is in a range of 1 to 6.